In live dramatic performances controlled lighting is often used to illuminate a performer or other item of interest. The illuminated area for live dramatic performance is conventionally a circular beam of light called a "spot light." This spot light has been formed from a bulb reflected by a spherical, parabolic, or ellipsoidal reflector. The combination forms a round beam due to the circular nature of reflectors and lenses.
The beam is often shaped by gobos. FIG. 1 shows a light source 100 projecting light through a triangular gobo 108 to the target 105. The metal gobo 108 as shown is a sheet of material with an aperture 110 in the shape of the desired illumination. Here, that aperture 110 is triangular, but more generally it could be any shape. The gobo 108 restricts the amount of light which passes from the light source 100 to the imaging lenses 103. As a result, the pattern of light 106 imaged on the stage 105 conforms to the shape of the aperture 110 in the gobo 108.
Light and Sound Design, the assignee of this application, have pioneered an alternate approach of forming the gobo from multiple selected reflective silicon micromirrors 200. One such array is called a digital mirror device ("DMD") where individual mirrors are controlled by digital signals. See U.S. Pat. No. 5,828,485 (application Ser. No. 08/598,077) and application Ser. No. 09/145,314, the disclosures of which are herein incorporated by reference. DMDs have typically been used for projecting images from video sources. Because video images are typically rectangular, the mirrors of DMDs are arranged in a rectangular array of rows and columns.
The individual mirrors 200 of a DMD are rotatable. Each mirror 200 is mounted on a bar 204 such that it can rotate in place around the axis formed by the bar 204. Using this rotation, individual mirrors 200 can be turned "on" and "off" to restrict the available reflective surface.
FIG. 2 shows an example of using a DMD 400 to project a triangular illumination by turning "off" some of the mirrors in the DMD 400. The surface of the DMD 400 exposed to a light source 402 comprises three portions. The individual mirrors which are turned "on" (toward the light source 402) make up an active portion 404. In FIG. 4A, the active portion 404 is triangular. The individual mirrors which are turned "off" (away from the light source 402) make up an inactive portion 406. These pixels are reflected. The third portion is a surrounding edge 408 of the DMD 400. Each of these portions of the DMD 400 reflects light from the light source 402 to different degrees.
FIG. 3 shows a resulting illumination pattern 410 with the active area 404 inactive area 406 and cage 408.